The Cheetahs and the Kings will join the Pro14 for the beginning of the season in September

A deal to expand the Pro12 to 14 teams from next season has been agreed, BBC Scotland understands.

The South African sides Cheetahs and Southern Kings will join the league after losing their Super Rugby status.

The six-year deal is likely to benefit the league to the tune of an extra £6m per season from the South African Rugby Union and additional television income.

All elements of the deal have been agreed and, once legally ratified, could be formally announced next week.

The new Pro14 league will kick-off in the first week of September and will comprise two conferences of seven teams. Each conference will have one Scottish side, one South African side, one Italian side and two each from Wales and Ireland.

The current preference is for two conferences of seven teams playing each other home and away. Within this format, the teams would also play one game against all the sides from the other conference, which would deliver 19 fixtures.

Additionally, each club would also play home and away derby fixtures as well, providing a total of 21 league games. However, other formats are also being discussed.

The winners of each conference will qualify automatically for the semi-finals, while the teams placed in second and third in each conference will be drawn together in play-offs for the remaining two semi-final places.

The Pro12 currently raises around £12m in television revenues, meaning the addition of the two South African sides represents a significant uplift as the Scottish, Irish and Welsh rugby unions try to bridge the financial gap to the English Premiership and French Top 14 teams.

The increase equates to around £500,000 in additional income per season for the existing Scottish, Irish, Welsh and Italian sides in the Pro12.

The Cheetahs and the Southern Kings are the weakest of South Africa's Super Rugby teams, and they were cut from next season's competition, opening the way for the move to join the Pro12.

One of the anticipated clauses for the deal is that the two franchises will commit to strengthening their squads, to ensure the competitive nature of the competition is protected.