Tau’s move to the EPL was confirmed on Friday as the Witbank-born player left the reigning Premier Soccer League (PSL) champions after four years.
Although the figures were not announced by the club, it is believed that the deal was worth R50 million.
Speaking after the move was announced by the two clubs, Mosimane said he was happy that a South African player has joined an English club.
He added that the move will come back to help Bafana Bafana and said he hoped Tau will cope in Europe.
The Brazilians will now prepare for life without the ‘Lion King’ as they look to continue dominating the South African Premier League and the African continent.
However, Tau will now be sent out on loan by the Seagulls to gain experience following a protracted transfer negotiation, especially between the Chloorkop-based side and Tau’s representatives.
“He deserved to be there. We said he should join a club in the top five leagues in Europe, we did not budge,” said Mosimane to the SABCSport.
“He didn’t understand sometimes, but he is smiling now. It’s what you do at the end... it’s not how you start,” he added.
“He is smiling now and he can be happy with everybody now that he has gone to the English Premier League - that’s what we wanted. We need to have somebody there,” he continued.
"South Africa must have someone and hopefully he represents us well there and then the others can follow,” Mosimane responded.
"You know how it is, when one goes, the rest will follow and we wish him all the best of luck, all the success because he is not representing Sundowns, but South Africa and he must come here and play for Bafana Bafana,” he concluded.