The husband of Robert F. Kennedy's granddaughter, Maeve, has paid heartbreaking tribute to his wife and young son a day after they disappeared while kayaking on Chesapeake Bay in Maryland.

In a Facebook post penned late Friday, David McKean claimed it was all but certain his wife Maeve Kennedy Townsend McKean, 40, and their son Gideon, eight, had drowned after they went out on the water to fetch a missing ball on Thursday afternoon.

'Maeve was my everything,' David wrote. 'She was my best friend and my soulmate. I have already thought many times over today that I need to remember to tell her about something that's happening. I am terrified by the idea that this will fade over time.'

David and Maeve were married in 2009. In addition to Gideon, the couple also share two younger children - daughter, Gabriella, seven, and son, Toby, two.

Maeve is a public health and human rights lawyer who serves as executive director of the Georgetown University Global Health Initiative. She graduated from the prestigious Washington, D.C. college with a law degree.

Maeve Kennedy Townsend McKean, 40, and her son Gideon, eight, are feared to have drowned Thursday while kayaking on Chesapeake Bay

Meave and husband David McKean are pictured with their three children, Gideon, Gabriella and Toby in a recent Facebook snap

Meave and David with their three children in a recent photo

David shared his heartbreaking post to Facebook after the Coast Guard called off the search for his wife and young son

In his Facebook post, David explained that he and Maeve had decided to take their children to a family lakehouse in Shady Side, Maryland to give them more space to play during the coronavirus lockdown.

'Maeve and Gideon were playing kickball by the small, shallow cove behind the house, and one of them kicked the ball into the water. The cove is protected, with much calmer wind and water than in the greater Chesapeake. They got into a canoe, intending simply to retrieve the ball, and somehow got pushed by wind or tide into the open bay,' David stated in his post.

About half an hour later, the mother and son were spotted far from the shore by a neighbor, and the police were promptly called.

'After that last sighting, they were not seen again. The Coast Guard recovered their canoe, which was capsized and miles away, at approximately 6:30 yesterday evening,' David somberly stated.

Meave and David are pictured with their three children in a photo taken last Halloween

The family-of-five are pictured at another relative's graduation ceremony last summer

Maeve and David were spending time with their three children at the family lakehouse in Shady Side, Maryland (above) when the tragedy occurred

The family is usually based in Washington DC, but had moved to a family lakehouse in Shady Side amid the coronavirus crisis

THE KENNEDY CURSE: TRAGEDIES THAT ROCKED AMERICA'S MOST FAMOUS FAMILY November 1963: President John F. Kennedy is assassinated in Dallas, Texas at the age of 46 June 1968: Senator Robert F. Kennedy - who was campaigning to be the Democratic nominee in that year's Presidential Election - is assassinated in Los Angeles at the age of 42 Curse: Senator Robert F. Kennedy was assassinated in Los Angeles at the age of 42 April 1984: Robert F. Kennedy's son, David Kennedy, dies of a drug overdose age 28 December 1997: Robert F. Kennedy's son, Michael Kennedy, dies in a skiing accident age 39 July 1999: President John F. Kennedy's son, John F. Kennedy Jr, dies in a plane crash alongside his wife Carolyn Bessette in a plane crash at the age of 38 September 2011: Senator Edward Kennedy's daughter, Kara Kennedy, dies of a heart attack age 51 May 2012: The wife of Robert F. Kennedy's son, Robert F. Kennedy Jr, commits suicide at the age of 52 August 2019: Robert F. Kennedy's granddaughter, Saoirse Kennedy Hill , dies of a drug overdose age 22 Camelot: President John F. Kennedy's son, John F. Kennedy Jr. and his wife Carolyn, died in a plane crash in 1999 Advertisement

He went on to pay tribute to his oldest child, Gideon.

'Gideon was 8, but he may as well have been 38. He was deeply compassionate, declining to sing children's songs if they contained a hint of animals or people being treated cruelly. He hated if I accidentally let a bad word slip. He spent hours upstairs reading, learning everything he could about sports, and trying to decipher the mysteries of the stock market. But he was also incredibly social, athletic, and courageous,' he wrote.

'I used to marvel at him as a toddler and worry that he was too perfect to exist in this world. It seems to me now that he was.'

David paid tribute to oldest son Gideon, eight, who is thought to have drowned along with his mother Thursday

David then turned his thoughts to Maeve, whom he married 11 years ago.

'She was my best friend and my soulmate... You could hear Maeve's laugh a block away—and she laughed a lot. She was magical—with endless energy that she would put toward inventing games for our children, taking on another project at work or in our community, and spending time with our friends,' he stated.

'She did the Peace Corps, she ran the Boston Marathon, she knew how rub Gabriella's legs when they cramped, and being in her presence somehow allowed you to be a better version of yourself. She was the brightest light I have ever known.'

If Maeve and Gideon are not discovered safely, David will face raising his two younger children as a single father.

'At seven, Gabriella is heartbroken, but she amazes me with her maturity and grace. Toby is two-and-a-half, so he's still his usual magical and goofy self. I know soon he will start to ask for Maeve and Gideon. It breaks my heart that he will not get to have them as a mother and brother,' he penned.

David then poignantly wrote: 'As Gabriella and Toby lay sleeping next to me last night, I promised them that I would do my best to be the parent that Maeve was, and to be the person that Gideon clearly would have grown up to be. Part of that is keeping their memories alive'.

'You could hear Maeve's laugh a block away—and she laughed a lot. She was magical—with endless energy': David wrote poignantly about his wife Meave (pictured after a recent marathon)

Maeve's mother is Kathleen Kennedy Townsend, who served as Maryland's sixth lieutenant governor from 1995 until 2003.

Kennedy Townsend released her own statement about the presumed death of her daughter on Friday night.

'With profound sadness, I share the news that the search for my beloved daughter Maeve and grandson Gideon has turned from rescue to recovery'.

Meanwhile, Maeve's cousin and Massachusetts Senate hopeful, Joe Kennedy III, also released a statement.

'We love you Maeve. We love you Gideon. Our family has lost two of the brightest lights,' he wrote on Twitter, fearing the worst.

New York Governor Andrew Cuomo was married to Maeve's aunt, Kerry Kennedy.

On Saturday, Governor Cuomo's daughter, Michaela Kennedy Cuomo, also shared her personal tribute.

'Maeve (my cousin) and Gideon (her son) had smiles that burst through their eyes and bought joy to all those around them,' 22-year-old Michaela wrote.

'Not being able to hold loved ones close and be together is crushing.'

McKean's mother, former Maryland Lt. Gov. Kathleen Kennedy Townsend, is the eldest daughter of the late Robert F. Kennedy and niece of the late President John F. Kennedy. Kathleen and Maeve are pictured above in 1995

Andrew Cuomo's daughter Michaela Kennedy Cuomo paid tribute to missing cousin Maeve and her son Gideon. Michaela and Gideon are pictured

Maryland's Governor Larry Hogan addressed the pair's disappearance during a coronavirus briefing on Friday, during which he offered sympathies to the family.

'I reached out to and spoke with Lt. Gov. Townsend this morning and on behalf of the people of Maryland I expressed our most heartfelt sympathies and prayers to her and to her entire family during this difficult time,' Hogan said.

Last week, Maeve had tweeted a photo of her son Gideon as she home-schooled him during the coronavirus pandemic.

The photo showed the eight-year-old smiling as he watched an interview between Stephen Curry and Dr Anthony Fauci - the nation's top coronavirus expert.

'@StephenCurry30 and Dr. Fauci's very informative interview was part of my 8-year old son's homeschooling today! #ParentingInAPandemic,' she tweeted alongside the photo.

Maeve, who is the executive director of the Georgetown University Global Health Initiative, had tweeted a photo of her son Gideon just last week as she home-schooled him during the coronavirus pandemic

The disappearance of the mother and son is the latest tragedy to involve the Kennedy family.

It comes less than a year after Saoirse Kennedy Hill, another of Robert F Kennedy's granddaughters, died from an overdose at the age of 22.

Among the prescription drugs found in her system were diazepam and nordiazepam (first marketed as Valium), fluoxetine (Prozac) and norfluoxetine (the anti-depressant Luoxetine).

Her death came just one month before she was set to start her senior year at Boston College.

Saoirse, who was the daughter of Courtney Kennedy Hill, is Maeve's cousin.