David Marcus, who runs the PayPal online payments service for eBay, is moving to Facebook to become head of its messaging products.

He has been at PayPal for three years, coming to eBay after it bought his payments startup, Zong.

This is a very big Silicon Valley poach by Facebook, which came after several discussions between Marcus and CEO and co-founder Mark Zuckerberg. It’s also a clear indication — especially given Marcus’s payments background — that the company intends to begin to monetize its messaging products.

John Donahoe, CEO of eBay, confirmed the departure in a very gallant post that read, in part: “As the head of PayPal for the past two years, David reinvigorated product design to deliver compelling consumer experiences and energized the team to make a great business better. An entrepreneur at heart, David has made a career decision to focus on what he loves most — leading smaller teams to create great product experiences.”

There has been speculation, for example, that users would eventually be able to attach digital cash to Facebook messages. But the company could use its popular messaging product in a number of different ways.

The social network said it now processes 12 billion messages on its Facebook Messenger daily. It has 200 million monthly active users of its app, which can be used separately from the network, but is also deeply integrated within it.

In his new job, Marcus will not have purview over WhatsApp, the global messaging product that Facebook recently bought for over $19 billion. That will be run independently.

Marcus posted on Facebook about the move, noting: “I thought long and hard about how I could express the range of emotions that are going through me as I write this post, and to put it simply … it’s hard.”

Well, not that hard, apparently!

Here is the whole post by Marcus:

I thought long and hard about how I could express the range of emotions that are going through me as I write this post, and to put it simply … it’s hard. After leaving a world I knew well — startups, and entrepreneurship — I joined PayPal about 3 years ago through its acquisition of my company, Zong. In the first instance running mobile, and eventually the leadership role at the company. I fell in love with it, its people, and the immense opportunity ahead. Going from managing a few hundred people at best in my entrepreneurial career, I suddenly found myself leading 14,000. The first year took its toll on me. It was hard. The second year started becoming more “natural,” and as we made progress on a number of fronts: technology, product, marketing, sales, and more importantly culture. I realized that my role was becoming a real management one, vs. my passion of building products that hopefully matter to a lot of people. So after much deliberation, I decided now is the right time for me to move on to something that is closer to what I love to do every day. Now is the time, because I feel that PayPal has never been in a better position to capitalize on its unique place in the market. Now is the time, because the product pipeline is strong, and these new experiences are scaling out. Now is the time, because PayPal’s reputation with developers is getting better by the day, because Braintree’s acquisition will truly enable PayPal to win in that space. Now is the time, because the leadership team is strong, and talent is flowing into the company again. In summary, now is time because PayPal is on track to achieve the greatness it deserves in the years to come. The hardest thing for me in my (painful) thought process was around the amazing people at PayPal I’ve been blessed to work with in the last 3 years. My direct team, who are the most brilliant people I’ve ever worked with. And while we worked real hard, we had our share of laughter, and fun. I’m going to miss them so much, and it’s so hard to imagine what my new life is going to be without them. Also, the rest of the team. The 14,000-strong team of unbelievably passionate people that makes this company so vibrant. I’m going to miss you all so dearly. But I find solace knowing you’re the guardians of what is one of the most extraordinary companies that was ever created. This wouldn’t be complete without thanking John Donahoe, who took a bet putting me in charge of PayPal a little over 2 years ago. John, you’ve been nothing but amazing to me. Thank you for the opportunity and the guidance you’ve given me all along this extraordinary journey. While I was in the middle of my thought process about what was next for me, Mark Zuckerberg and I got together. Mark shared a compelling vision about Mobile Messaging. At first, I didn’t know whether another big company gig was a good thing for me, but Mark’s enthusiasm, and the unparalleled reach and consumer engagement of the Facebook platform ultimately won me over. So … yes. I’m excited to go to Facebook to lead Messaging Products. And I’m looking forward to getting my hands dirty again attempting to build something new and meaningful at scale. PayPals, you will always be in my heart. Know that I’ll be a proud witness of your wins, and successes.