Midfielder Sanches has signed a five-year contract with the German champions after passing a medical on Monday – and Bayern quickly followed up that announcement with the news that Hummels will also be joining the club.
Hummels, who started his career with Bayern before joining Dortmund in 2008, initially on loan, will return to the German champions on a deal until 2021, joining former team-mates Robert Lewandowski and Mario Gotze at the club.
Sanches, 18, scored against Bayern in the Champions League quarter-finals last month, and is tipped to impress for Portugal at Euro 2016 in France.
According to reports United had scouted the player for 22 games, but he has gone to Bayern for an initial fee of €35m – which is complemented by potential add-ons of €45m making him one of the most expensive teenagers in history with a total package of £63m.
He was Bayern’s first signing of the close season – beating Hummels to the punch by mere minutes – as they prepare for life under new coach Carlo Ancelotti with Pep Guardiola heading for Manchester City.
Sanches signed a lengthy contract with Benfica back in 2011, but it was clear they would have trouble keeping him after he impressed in his first full season in the first team.
“Renato Sanches has been observed over a long period by Bayern,” said Bayern CEO Karl-Heinz Rummenigge. “We are fortunate to have signed him despite well-known international competition. “Renato is a dynamic, combative and technically gifted midfielder who will strengthen our team further.”