Lol no Sentinel. That's his coach Lennart Bergelin back in about 1978 or so. He was instrumental in Borg's career. Borg was the first player to begin this trend of having a coach travel with one player exclusively to all tournaments. That is common now yet again Borg was a trendsetter. Lennart Bergelin died in 2008 at 83 and Borg was very close to him, considering him like a second father. I'll email you a picture of me on the tennis court.
